In short - all of your ideas are on the right path.
If you’re in the US, consider a class in community college. My CC have one combined piano + music 1. The teacher will guide you to next steps too. CC is inexpensive and a teacher is better (I think) than any course you find online.
I personally went from taking Music 1 out of curiosity to taking every theory, piano, viola, percussion… that was on offer in my CC over the last 6 years. Highly addictive.